#include <iostream>
using namespace std;

int main(){
	double sum = 0;
  	for(int i =1;i<=12;i++){
      	double t;
      	cin >> t;
      	sum = sum + t;
    }
  	cout << "$";
  	cout << fixed << setprecision(2) << sum / 12 << endl;
	return 0;
}